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Why Are Primaries Hard to Predict?

By Andrew Gelman November 29, 2011 12:26 amNovember 29, 2011 12:26 am

Presidential elections are predictable. At the national level, economic conditions — measures like the change in per-capita income in the year or so preceding the election — usually do a good job predicting the popular vote. At the state level, you can usually predict the outcome given the vote last time, after adjusting for the economy and the home states and regions of the candidates. At the level of individual voters, preferences are largely predictable from political ideology, degree of partisanship, and, again, recent economic conditions.

In 1993, Gary King and I wrote a paper, “Why are American presidential election campaign polls so variable when votes are so predictable?” Our answer was that early polls are not very meaningful and that during the election campaign voters tend to move toward their predictable positions. Fluctuations during the campaign (for example, the well-documented “bump” that candidates receive during their nominating conventions) are part of a shaking-out process, and it makes sense to look toward where the polls will end up at election time rather than at the changes that happen to occur during any particular week of the campaign.

But even though statistical analysis has demonstrated that presidential elections are predictable given economic conditions and previous votes in the states, (go here for an analysis I did with Kari Lock that uses state-level poll data), it certainly doesn’t mean that everyelection can be accurately predicted ahead of time.

Presidential general election campaigns have several distinct features that distinguish them from most other elections:

1. Two major candidates;
2. The candidates clearly differ in their political ideologies and in their positions on economic issues;
3. The two sides have roughly equal financial and organizational resources;
4. The current election is the latest in a long series of similar contests (every four years);
5. A long campaign, giving candidates a long time to present their case and giving voters a long time to make up their minds.

Other elections look different. In Europe, for example, the major parties of the left and the right are not so distinct on economic policies, and there are typically three or more major parties competing. Referenda in American states typically feature highly unequal campaigns with one side much better funded than the other. In addition, referenda typically address new issues so that you cannot predict the outcome based on previous elections on the same topic. Campaigns for governor, senator and the House are also often highly unbalanced in resources.

And while presidential elections are predictable, the nominating contests that choose the candidates are not. Presidential primaries often have none of the five features I mentioned earlier. With three or more candidates, there is an incentive for strategic voting (not wanting to waste your vote on a candidate who doesn’t have a chance); this creates a positive feedback or “bandwagon” effect in which strong candidates get stronger and weak candidates disappear, an effect that we do not see in two-candidate contests.

The candidates in a primary election are of the same political party and typically differ in only minor ways in their political positions, so it is easier for voters to change their opinions. Primary election campaigns can be highly unequal too, with different candidates pouring their efforts into different states. And during the heat of primary season, voters may have only a week or two to make up their minds in light of the news from the most recent primaries elsewhere.

As a result, it’s no surprise that primaries are unpredictable. Once the dust clears, though, we get to a general election campaign that, for all the noise, is mostly determined by the state of the economy. Yes, “it’s the economy, stupid” when November comes along — a fact that has driven many of the economic and political calculations of President Obama and congressional Republicans over the past few years — but the primaries tell their own story.

Andrew Gelman is a professor of statistics and political science at Columbia University and the author of “Red State, Blue State, Rich State, Poor State: Why Americans Vote the Way They Do.”

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Weekly pieces by the Op-Ed columnists Charles Blow and Ross Douthat, as well as regular posts from contributing writers like Thomas B. Edsall and Timothy Egan. This is also the place for opinionated political thinkers from all over the United States to make their arguments about everything connected to the 2012 election. Yes, everything: the candidates, the states, the caucuses, the issues, the rules, the controversies, the primaries, the ads, the electorate, the present, the past and even the future.